Yamahara Kevan M, Layton Blythe A, Santoro Alyson E, Boehm Alexandria B
Department of Civil and Environmental Engineering, Environmental and Water Studies, Stanford University, Stanford, California 94305-4020, USA.
Environ Sci Technol. 2007 Jul 1;41(13):4515-21. doi: 10.1021/es062822n.
Fecal indicator bacteria (FIB) are nearly ubiquitous in California (CA) beach sands. Sands were collected from 55 beaches along the CA coast. Ninety-one percent of the beaches had detectable enterococci (ENT) while 62% had detectable E. coli (EC) in their sands. The presence of a putative bacterial source (such as a river), the degree of wave shelter, and surrounding land use explained a significant (p < 0.05) fraction of the variation in both ENT and EC densities between beaches. Sand characteristics including moisture content, organic carbon, and percentfines, significantly (p < 0.05) influenced only EC densities in beach sand. We assayed 34 of 163 sand samples for salmonellae, but did not detect this bacterial pathogen. The potential for FIB to be transported from the sand to sea was investigated at a single wave-sheltered beach with high densities of ENT in beach sand: Lovers Point, CA (LP). We collected samples of exposed and submerged sands as well as water over a 24 h period in order to compare the disappearance or appearance of ENT in sand and the water column. Exposed sands had significantly higher densities of ENT than submerged sands with the highest densities located near the high tide line. Water column ENT densities began low, increased sharply during the first flood tide and slowly decreased over the remainder of the study. During the first flood tide, the number of ENT that entered the water column was nearly equivalent to the number of ENT lost from exposed sands when they were submerged by seawater. The decrease in nearshore ENT concentrations after the initial influx can be explained by ENT die-off and dilution with clean ocean water. While some ENT in the water and sand at LP might be of human origin because they were positive for the esp gene, others lacked the esp gene and were therefore equivocal with respect to their origin. Follow-up sampling at LP revealed the presence of the human specific Bacteroides marker in water and sand.
粪便指示菌（FIB）在加利福尼亚州（CA）的海滩沙子中几乎无处不在。从加利福尼亚州海岸的55个海滩采集了沙子样本。91%的海滩沙子中可检测到肠球菌（ENT），而62%的海滩沙子中可检测到大肠杆菌（EC）。假定的细菌源（如河流）的存在、波浪遮蔽程度和周边土地利用情况，在很大程度上（p < 0.05）解释了不同海滩之间肠球菌和大肠杆菌密度变化的部分原因。包括含水量、有机碳和细粒百分比在内的沙子特性，仅对海滩沙子中的大肠杆菌密度有显著（p < 0.05）影响。我们对163个沙子样本中的34个进行了沙门氏菌检测，但未检测到这种细菌病原体。在一个海滩沙子中肠球菌密度很高的波浪遮蔽海滩——加利福尼亚州的情人岬（LP），研究了粪便指示菌从沙子转移到海洋的可能性。我们在24小时内采集了暴露和淹没沙子以及水的样本，以比较沙子和水柱中肠球菌的消失或出现情况。暴露沙子中的肠球菌密度显著高于淹没沙子，最高密度位于高潮线附近。水柱中的肠球菌密度开始时较低，在第一次涨潮期间急剧增加，在研究的其余时间缓慢下降。在第一次涨潮期间，进入水柱的肠球菌数量几乎相当于暴露沙子被海水淹没时损失的肠球菌数量。初始涌入后近岸肠球菌浓度的下降可以通过肠球菌死亡和被清洁海水稀释来解释。虽然情人岬水和沙子中的一些肠球菌可能来自人类，因为它们的esp基因呈阳性，但其他肠球菌缺乏esp基因，因此其来源不明确。情人岬的后续采样显示，水和沙子中存在人类特异性拟杆菌标记物。
